Partial molar pregnancy after pathology negative

Jamie • Married to my best friend. Ectopic January 18. MC August 18. PMP October 18.Mom to two fur babies 🐱

So I found out I was pregnant September 17,2018. I had an ultrasound at 5+6 saw sac and fetal pole went at 7+6 baby measuring 7+1 and heartbeat of 144 and everything looked great. Two days later I started spotting and they did an ultrasound and found the baby’s heartbeat stopped. Waited 1 week and had d&c. Pathology was normal but testing came back as triploidy. 8 weeks after first d&c had severe bleeding so had 2nd d&c on December 19,2018 for retained tissue. Again pathology came back normal. Dr has watched my hcg and we had got to 14 then the past two draws were 16 and then 21. He has referred me to the ob oncologist and said they would treat with methotrexate. I just don’t know how both pathology can be normal but now having rising hcg. Has anyone have this happen? And any advice on the methotrexate. My normal ob sent me for a chest X-ray not sure why but they said it was normal. I’m very worried and confused this has been the longest draining 15 weeks. I just keep thinking I should be 24 weeks pregnant and I’m still dealing with this.